Likely to originate in WWI/WWII era with "Devil Dogs", "dogface", and similar terms.

Evolved to become slang in the 1960s through current times for specific jobs, ie. "wire dogs" for Army communications soldiers running wire reels; "demo dogs" for Army combat engineers with explosive demolition; "water dogs" for USMC water purification specialists; et al.

Also used in unofficial unit nicknames, such as "3rd Platoon Mountain Dogs", "Delta Dogs", and unit official nicknames such as USN Strike Squadron 105 "Mad Dogs".